The visual perception of color is known to be a highly subjective phenomenon, difficult to investigate empirically. This is due in part to the highly erratic response of subjects to color stimulus, because of complex psychological and physiological factors. It is also due to the rather inexact nature of the color perception testing procedures known in the prior art.
Most color vision testing procedures involve the use of dot matrices or color bar designs printed on display cards and shown to the test subject. In most testing procedures, the illumination of the display is not monitored for color value or intensity, nor are the ambient light conditions controlled. Other testing devices which employ illuminated color filter combinations are similarly errant in their lack of control of the lighting conditions of the examination. Furthermore, no device in the prior art is capable of maintaining a constant luminance level while varying the hue and saturation of the output signal.